Cataract, or clouding of the natural lens of the eye, is the leading cause of preventable blindness in the world. Presently, cataracts are treated by surgical removal of the affected lens and replacement with an artificial intraocular lens (“IOL”). FIG. 1 is a diagram of an eye 100 illustrating anatomical structures related to the surgical removal of a cataract and the implantation of an IOL. The eye 100 comprises a lens 102, an optically clear cornea 104, and an iris 106. A lens capsule (capsular bag 108) located behind the iris 106 of the eye 100 contains the lens 102. More particularly, the lens 102 is seated between an anterior capsule segment (anterior capsule 110) and a posterior capsular segment (posterior capsule 112). The anterior capsule 110 and the posterior capsule 112 meet at an equatorial region 114 of the capsular bag 108. The eye 100 also comprises an anterior chamber 116 located in front of the iris 106 and a posterior chamber 118 located between the iris 106 and the capsular bag 108.
A common technique for cataract surgery (including removal of an opacified lens 102) is extracapsular cataract extraction (“ECCE”). ECCE involves the creation of an incision near the outer edge of the cornea 104 and an opening in the anterior capsule 110 (i.e., an anterior capsulotomy) through which the opacified lens 102 is removed. The lens 102 can be removed by various known methods. One such method is phacoemulsification, in which ultrasonic energy is applied to the lens to break it into small pieces that are aspirated from the capsular bag 108. Thus, with the exception of the portion of the anterior capsule 110 that is removed in order to gain access to the lens 102, the capsular bag 108 may remain substantially intact throughout an ECCE. The intact posterior capsule 112 provides a support for the IOL and acts as a barrier to the vitreous humor within the posterior chamber 120 of the eye 100. Following removal of the opacified lens 102, an artificial IOL may be implanted within the capsular bag 108 through the opening in the anterior capsule 110. Implanted IOLs are typically monofocal lenses that provide a suitable focal power for distance vision but require the use a pair of spectacles or contact lenses for near vision. Multifocal IOLs relying on diffractive patterns to generate multiple foci, are also available but to date have not been widely accepted.
In a healthy eye, zonular forces are exerted by ciliary muscles 122 and attached zonules 124 surrounding the periphery of the capsular bag 108. These forces change the shape of the natural lenses, thereby changing its power and allowing a clear focus on an image as its distance varies. When monofocal or diffractive multifocal IOLs are implanted, this natural accommodative ability of the eye is lost.
Therefore, a need exists for a safe and stable accommodative intraocular lens that provides accommodation over a broad and useful range.